“JFK’s Last Hundred Days” is the title of a book about that time in the life of President John Fitzgerald Kennedy. The author, Thurston Clarke, has written for magazines, as well as works of fiction.

And he has made full use of material made available at the Kennedy Library, as well as comments by people who participated in that administration. Some of the information is familiar, but others — I, at least — had not known about.

While the book’s chapters follow the chronology of those hundred days leading up to the assassination in Dallas, the material contained in the chapters takes in considerably more time.

There were hawks and doves in the Kennedy White House, and the author makes it clear that JFK himself came to be pretty much on the dove side. He spoke quite clearly about getting out of Vietnam completely, but didn’t want to make such a definite move until after the 1964 elections.

He was pretty certain the Republicans would nominate Barry Goldwater, and he didn’t want to give Goldwater the chance to accuse him of being “soft.” He spoke about a drastic reduction in U.S. personnel in Saigon by the end of 1965. If he had lived to put that into effect, the shape of this country’s politics during the next couple of decades would have been considerably different.

The days spent on family matters are also covered in the book. Given the personalities involved, theirs was not the smoothest family life, but they tried to keep it placid on the surface. The Kennedys had lost their second son, born prematurely and soon dead, but the president did cavort with his other two children when he had a chance.

Kennedy, of course, had worked out a treaty for reduction of nuclear weapons with Nikita Khrushchev of the Soviet Union. What I hadn’t realized was the impact on the administration of a best-selling novel that had come out the year before. “Seven Days in May” is about a coup attempt by U.S. military figures in the future against a president who has signed a nuclear treaty with the Soviets.

One of the novel’s authors, Fletcher Knebel, had interviewed military personnel at the Pentagon and had found some who were very dissatisfied with Kennedy, particularly since he refused to have U.S. forces support the Cuban rebels in the Bay of Pigs incident. An Air Force general, Curtis LeMay, went so far as to call Kennedy a coward. Several admirals also were unhappy at White House attitudes.

Kennedy told friends that he thought there might be a coup attempt against his administration, but only if there were another Bay of Pigs incident, and he wasn’t planning on having any such thing take place. During conferences, he often doodled on scratch paper, and on several of such sheets that have been saved, he scribbled the word “coup.” Sometimes, the context seemed to be about a coup in Saigon, but at other times, he seemed to be thinking about matters much closer to home.

His brother, Robert, the attorney general, went so far as to tell Soviet Ambassador Anatoly Dobrynin that a U.S. military coup was actually being thought of, but that seems to have been merely an effort to get the Soviets to move faster on the arms treaty.

It may well have been afterthoughts, but a number of people claimed that they told Kennedy not to go to Dallas. His civil-rights activity had angered many in the South. One emissary he sent there, Adlai Stevenson, had been battered by people carrying anti-administration placards.